Within the field of the automotive aftermarket, there are numerous parts that are considered to be “non-serviceable” items. In such cases, a new part must be purchased at a substantial cost to the end user. In the field of automatic transmissions, one such common device is the solenoid module assembly that controls hydraulic flow and pressure within the transmission. A typical solenoid module consists of a hydraulic manifold and one or more electromechanical solenoids. The hydraulic manifold contains numerous fluid circuit passages that hydraulically communicate with the solenoids. The electromechanical solenoids control either the flow (on/off control) through the passages or regulate pressure within the passages. Typically, the solenoids are electrically connected to a terminal housing that provides for a removable connection to a wire harness, allowing for communication to the powertrain control unit (PCU).
One such assembly is described in U.S. Pat. Nos. 4,687,006 and 4,783,049. In the described invention, a device consisting of five electrically actuated solenoid assemblies are situated on an aluminum manifold block consisting of multiple fluid passageways. The connections for the solenoids consist of round pins that extrude upwards through a printed circuit board (PCB) and are soldered into place. The PCB interconnects to a terminal connector providing communication through a wire harness to the PCU. This particular solenoid module has been used in the Ford E4OD and 4R100 automatic transmission since 1989. It has several well-known failure modes and is a common replacement item. These new modules typically cost $150-200 to the end user. Several companies rebuild these modules by disassembling the unit, cleaning and replacing defective components. A new PCB of similar configuration to the original is soldered into place. A rebuilt unit costs approximately $100 to the end user.
A response curve for a typical solenoid is shown in FIG. 1. Here, the output pressure is shown as the current increases and subsequently decreases.
During a typical life cycle of the above described EPC, there are several components that can degrade. However, as background for some of the embodiments of the present invention, the wear in the hydraulic housing and spool valve will be discussed. The mechanical interface between spool valve and the bore of the hydraulic housing is important to the operation of the solenoid. The clearance between the spool valve and bore should be within certain operational limits. If the clearance is too small, the valve will not operate smoothly and can become encumbered by contamination in the fluid. If the clearance is too large, the valve will leak and the hydraulic operation can become erratic. A typical response curve for a used solenoid is shown in FIG. 2.
A common problem with certain solenoid designs, such as the E4OD/4R100 EPC, is inconsistent output response between increasing current and decreasing current, commonly referred to a hysteresis. A comparison of a low and high hysteresis is shown in FIG. 3 (for illustrative ease, the graph is focused in the low amperage range). Ideally, the decreasing output pressure curve would follow the same curve as the increasing output pressure (i.e., one curve would describe the increasing and decreasing current response). In the case of high hysteresis as shown in FIG. 3, the increasing and decreasing current response shows a wide discrepancy (wide band). For the low hysteresis, the difference between the two curves is close (narrow band).
There are several causes of the hysteresis, which can include contamination buildup in the solenoid, improper valve clearance, damage to the spool valve/hydraulic bore. Another source is mechanical “slop”, which is inherent to the solenoid design. This mechanical “slop” is from slight movement of the adjustment end of the solenoid. In the depicted solenoid, this movement can be from loose threads in the adjustment pieces or from movement of the backing plate to which the adjustment pieces are affixed. There are numerous ways to remove the mechanical movement in the threads, including using thread tape or sealant, or distorting the threads. The manufacturer of the solenoid may weld the adjustment pieces.